Skid steer vehicle having suspensions that are locked based on vehicle speed

Abstract

A skid steer vehicle includes a chassis mounted on four sprung suspensions that are controlled by an electronic controller. The controller monitors the speed of the vehicle and locks the suspensions when the vehicle falls below a predetermined speed.

What is claimed is:  
     
       1. A skid steer vehicle comprising: 
       a chassis having a left side and a right side;  
       an engine coupled to the chassis;  
       first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure;  
       four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation;  
       four control arms pivotally coupled to the chassis and coupled to the four wheels to permit the wheels to pivot at least in a vertical direction with respect to the chassis;  
       at least two hydraulic motors for driving the wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis;  
       four hydraulic cylinders, each cylinder operably coupled to one of the wheels to control at least the vertical position of the wheels with respect to the chassis;  
       a speed sensing means to provide a signal indicative of the speed of the vehicle over the ground; and  
       an electronic controller coupled to the speed sensing means and to the hydraulic cylinders that is configured to lock the four wheels in a vertical position with respect to the chassis when the vehicle falls below a predetermined speed.  
     
     
       2. The skid steer vehicle of  claim 1 , wherein the speed sensing means is one of a group consisting of a wheel speed sensor, a hydraulic pump control circuit configured to generate a signal indicative of pump position; a memory location in the electronic controller containing digital data indicative of the displacement of at least one of the first and second pumps. 
     
     
       3. The skid steer loader of  claim 2 , wherein the digital data indicative of the displacement is a value generated by the electronic controller. 
     
     
       4. The skid steer vehicle of  claim 2 , further comprising four valves, each of the four valves being coupled to one of the hydraulic cylinders to control an outflow of fluid from said one of the hydraulic cylinders. 
     
     
       5. The skid steer vehicle of  claim 4 , wherein the electronic controller is configured to automatically and repeatedly receive the signal indicative of the speed of the vehicle from the speed sensing means, to compare the signal indicative of the speed of the vehicle with a value indicative of a predetermined speed, and to close the four valves when the vehicle is below the predetermined speed. 
     
     
       6. The skid steer vehicle of  claim 5 , further comprising four gas-charged hydraulic accumulators, wherein each accumulator is fluidly coupled to and between one of the valves and said one of the valve's associated cylinder to block hydraulic fluid between the associated cylinder and said each accumulator. 
     
     
       7. A skid steer vehicle comprising: 
       a chassis having a left side and a right side;  
       an engine coupled to the chassis;  
       first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure;  
       four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation;  
       two control arms, each of the two control arms pivotally coupled to and between the chassis and an associated forward wheel to permit the associated forward wheel to pivot at least in a vertical direction with respect to the chassis;  
       at least two hydraulic motors for driving the wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis;  
       two hydraulic cylinders, each cylinder operably coupled to one of the two forward wheels to control at least the vertical position of said one of the two forward wheels with respect to the chassis;  
       a speed sensing means to provide a signal indicative of the speed of the vehicle over the ground; and  
       an electronic controller coupled to the speed sensing means and to the hydraulic cylinders that is configured to lock the two forward wheels in a vertical position with respect to the chassis when the vehicle falls below a predetermined speed.  
     
     
       8. The skid steer vehicle of  claim 7 , wherein the speed sensing means comprises one of a group consisting of at least one wheel speed sensor, a hydraulic pump control circuit configured to generate a signal indicative of hydraulic pump position, and a memory location in the electronic controller containing digital data indicative of a commanded displacement of at least one of the first and second pumps. 
     
     
       9. The skid steer loader of  claim 8 , wherein the digital data indicative of the commanded displacement is a value generated by the electronic controller to control the displacement of said at least one of the first and second pumps. 
     
     
       10. The skid steer vehicle of  claim 8 , further comprising two valves, each of the two valves being coupled to one of the hydraulic cylinders to control an outflow of fluid from said one of the hydraulic cylinders. 
     
     
       11. The skid steer vehicle of  claim 10 , wherein the electronic controller is configured to automatically and repeatedly receive the signal indicative of the speed of the vehicle from the speed sensing means, to compare the signal indicative of the speed of the vehicle with a value indicative of a predetermined speed, and to close the two valves when the vehicle is below the predetermined speed. 
     
     
       12. The skid steer vehicle of  claim 11 , further comprising two gas-charged hydraulic accumulators, wherein each accumulator is fluidly coupled to and between one of the two valves and said one of the two valves associated cylinder to block hydraulic fluid flow from the associated cylinder to said each accumulator. 
     
     
       13. A method of controlling the suspensions of a skid steer vehicle, the vehicle including: 
       a chassis having a left side and a right side;  
       an engine coupled to the chassis;  
       first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure;  
       four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation;  
       two control arms, each of the two control arms pivotally coupled to and between the chassis and an associated forward wheel to permit the associated forward wheel to pivot at least in a vertical direction with respect to the chassis;  
       at least two hydraulic motors for driving the wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis;  
       two hydraulic cylinders, each cylinder operably coupled to one of the two forward wheels to control at least the vertical position of said one of the two forward wheels with respect to the chassis;  
       a speed sensing means to provide a signal indicative of the speed of the vehicle over the ground; and  
       an electronic controller coupled to the speed sensing means and to the hydraulic cylinders that is configured to lock the two forward wheels in a vertical position with respect to the chassis when the vehicle falls below a predetermined speed, the method comprising the steps of:  
       reading the signal indicative of the speed of the vehicle;  
       comparing the signal indicative of the speed of the vehicle with a value indicative of a predetermined speed;  
       locking the two forward wheels of the four wheels to prevent vertical motion of the two wheels with respect to the chassis when the step of comparing indicates that the vehicle is traveling slower than the predetermined speed; and  
       unlocking the two forward wheels to permit vertical motion of the two wheels with respect to the chassis when the step of comparing indicates that the vehicle is traveling above the predetermined speed.  
     
     
       14. The method of  claim 13 , wherein the step of comparing includes the step of accessing an electronic memory location in the electronic controller having a value indicative of a commanded displacement of at least one of the first and second variable displacement pumps. 
     
     
       15. The method of  claim 13 , wherein the vehicle includes two valves, wherein each of said two valves is fluidly coupled to an associated one of the two hydraulic cylinders to control the outflow of fluid from said associated one of the two hydraulic cylinders, and further wherein each of said two valves is operably coupled to the electronic controller to be controlled thereby. 
     
     
       16. The method of  claim 15 , wherein the step of locking the two forward wheels includes the step of closing the two valves. 
     
     
       17. The method of  claim 16 , wherein the step of locking the two forward wheels includes the step of blocking fluid flow from the two cylinders to two associated hydraulic accumulators.